Powdered, granulated or other finely divided materials, such as carbon black, highly dispersed silica, or foodstuffs, such as flour, are shipped in bags provided with a filler valve which admits insertion of a filler nozzle and closes on withdrawal of the nozzle, i.e., removal of the bag from the filling machine. In most cases such valve bags are made of strong multi-layer paper.
It has been known to make the filler valve likewise of multi-layer relatively stiff paper. Such filler valves, however, have the disadvantage of frequently not closing completely with a consequent undesirable escape of the bag contents through the valve especially during transportation of the bag.
Attempts have been made to construct filler valves for valve bags which effectively prevent escape of the bag contents. An example is disclosed in German Pat. No. 2,363,753 wherein the length of the valve falls short of that of the filler nozzle. That valve, however, now only is relatively complex and costly to make but also requires the use of material more expensive than the multi-layer paper of which valve bags normally are made. Another example of an attempted improvement is disclosed in German Utility Pat. No. 1,870,373 wherein the inner end of the filler valve is provided with a flexible insert intended to close on withdrawal of the filler nozzle. In many cases, however, it does not, i.e. its closing action is unsatisfactory.